IO-Link strain gauge amplifiers for load cells and force transducers

IO-Link measuring amplifiers digitize the signal of a strain gauge full bridge directly at load cells or force transducers and transfer it to the controller as a standardized IO-Link signal. Without an analog input card, using unshielded standard cables and M12 connectors. Compact design from 72 x 28 x 35 mm, protection class at least IP65, measuring range freely adjustable.

How IO-Link measuring amplifiers change load cells or force transducers

A load cell provides a signal of a few millivolts. Traditionally, this signal is fed into the control cabinet via a shielded cable, amplified there and converted to 4…20 mA or 0…10 V, and then digitized again by an analog input card. Each of these steps costs accuracy, wiring effort, and space.

An IO-Link measuring amplifier places digitization at the beginning. It sits directly at the sensor, powers the measuring bridge, converts the signal with 16 bits, and transmits the value digitally. From this point on, the measured value is data and no longer an analog signal that could change along the way.

Practically, this means: no free analog card needed, unshielded standard cable instead of measurement cable, M12 connectors instead of terminals, and the resolution is no longer limited by the input card. The measuring range can be freely scaled from -32000 to +32000, so you can work directly in Newtons, Kilonewtons, or Kilograms. You can find basic information on the technology on our page about IO-Link.

The underestimated advantage: sensor replacement without rework

With analog evaluation, replacing a cell always means rework. The characteristic value and zero point of the new cell deviate, so recalibration or re-calibration with test weights is necessary, usually by someone who knows how to operate the device.

In an IO-Link system, parameters are stored in the master. If a device is replaced, the master automatically uploads the stored settings to the new device. Misconfigurations due to manual parameterization are eliminated, and replacement can be carried out by maintenance personnel without metrology knowledge. For series machine builders, the same mechanism is doubly valuable: all machines in a series receive identical parameters, reproducibly and documented.

Diagnostics and statistics from the device

IO-Link not only transmits measured values but also status information through a single cable. Depending on the device, minimum, maximum, peak value, operating hours counter, and load collective are available.

This opens up applications that are not possible with an analog signal. A load collective shows how often a component has been subjected to stress in which load range, and thus whether a press or lifting equipment is being operated within its design limits. A recorded peak value indicates an overload that had long disappeared in the cyclic process value. And the device diagnostics report cable breaks or sensor errors, instead of just providing an implausible value.

Two ways to an IO-Link load cell

Separate measuring amplifier at the sensor. The module is mounted near the existing cell and turns any strain gauge full bridge into an IO-Link device. This is the way for retrofitting and for cases where you want to keep the sensor type. Bridges from 350 ohms at 3 V supply are connected, the housing is protected with at least IP65 and small enough to sit in the machine frame instead of the control cabinet.

Cell with integrated electronics. Here, the amplifier is integrated into the sensor housing; there is only one device and one cable. This is the more compact and robust solution for new designs when there is no space for an additional module. All our load cells and force transducers can be equipped with IO-Link in this way; for special designs, we develop customized transducers with an integrated interface.

Commissioning

For integration, you upload the device's IODD file into your engineering tool, after which parameters and process data are available named and described. Scaling, zero point, and filter are set in the master, not on the device, which also means: no opening of housings and no potentiometers. IODD file, datasheet, and CAD model are available for download with each item.

Because IO-Link is standardized across manufacturers and fieldbus-independent, the devices work with common masters and controllers, regardless of whether PROFINET, EtherCAT, or another bus is used.

When IO-Link is not the right choice

Three cases argue against it, and it's better to know them beforehand.

Fast dynamic measurements. IO-Link transmits cyclically with a cycle time in the millisecond range. This is ample for weighing, dosing, force monitoring, and limit value control. If you want to record a force profile during an impact or joining process at a high rate, use a strain gauge measuring amplifier with appropriate bandwidth.

Long distances. IO-Link is a point-to-point connection with limited cable length. For the path from the silo outdoors to the control room, a weighing transmitter with bus or analog output is the appropriate solution.

A single weighing point without IO-Link infrastructure. If no master is available and an analog card is free, the analog solution is more cost-effective. IO-Link pays off as soon as several devices are connected to one master or the mentioned diagnostic and replacement advantages count.

The combination of cell and IO-Link amplifier is not intended for legal-for-trade applications; there, weighing indicators with corresponding approval are the way to go.

Typical applications

Press and joining force monitoring, press-fit processes with force-displacement evaluation, gripper and clamping force measurement in handling, tool and process monitoring, tank weighing within machines, overload monitoring on lifting equipment and fixtures, force measurement in testing equipment during ongoing production.

You can find sensors under load cells and force transducers and specifically under tension and compression force transducers, and further evaluation electronics under measurement electronics. So that you can measure in the unit of your application and not in mV/V, we calibrate the measuring chain according to ISO 17025 in our own laboratory, if desired.

Our engineers will advise you directly on the selection of amplifier, sensor, and scaling.